Quasi-planar homopolymetallic and heteropolymetallic coordination arrays. Surface-like molecular clusters of magnesium and aluminum.

The sterically isolated preorganized tetradentate ligand systems, tetrakis(2-hydroxy-3-n-propylphenyl)ethene and tetrakis(5-tert-butyl-2-hydroxy-3-trimethylsilylphenyl)ethene, nucleate the formation of quasi-planar raft-like polymetallic coordination complexes with high selectivity, providing topologically consistent structural models for metal coordination to the "oxo-surface" of silica- and alumina-supported heterogeneous catalysts. The coordination of magnesium salts to these systems yields trimetallic magnesium halide and alkyl complexes arrayed on the oxygen "surface" of the ligand, regardless of the steric profile of the ortho-substituents. The magnesium complexes, characterized in the solid state by X-ray crystallography, contain two chemically distinct metal environments, a relatively inert central magnesium bis(alkoxide) and two more labile pseudotetrahedral "wing" magnesium atoms. The central metal coordination is pseudo-octahedral; crystallography strongly suggests the presence of an unprecedented dative magnesium-olefin bonding interaction from the metal to ethene bridge of the ligand. Consistent with the chemistry proposed for typical magnesium-treated catalyst supports, the labile wing magnesium centers can be cleanly and sequentially exchanged for aluminum with retention of the surface-like coordination array. Thus, treatment with diethylaluminum chloride provides heterotrimetallic magnesium-aluminum complexes containing one aluminum and two magnesium sites or two aluminum and one magnesium site, respectively. All four heteropolymetallic complexes have been characterized by X-ray crystallography.

Ortho-silylated derivatives of tetrakis(2-hydroxyphenyl)ethene: a sterically isolated structural model for oxo-surface binding domains.

The introduction of sterically isolating ortho-trialkylsilyl, -aryldialkylsilyl, and -diarylalkylsilyl substituents onto the structurally preorganized tetrakis(2-hydroxyphenyl)ethene ligand framework has been accomplished by a 4-fold retro-Brook rearrangement. Installation of the most sterically demanding silyl substituents required the development of an iterative procedure, involving successive double silylation/metalation/migration sequences without the isolation of intermediates. This system was designed to function as a soluble structural model for the planar binding domains of heterogeneous "oxo-surfaces" of silica and alumina supports.